Python | Concatenate dictionary value lists

Sometimes, while working with dictionaries, we might have a problem in which we have lists as it’s value and wish to have it cumulatively in single list by concatenation. This problem can occur in web development domain. Let’s discuss certain ways in which this task can be performed.

Method #1 : Using `sum() + values()`
This is the most recommended method and one liner to perform this task. In this, we access all list values using `values()` and concatenation utility is performed using `sum()`.

 `# Python3 code to demonstrate working of ` `# Concatenating dictionary value lists ` `# Using sum() + values() ` ` `  `# initializing dictionary ` `test_dict ``=` `{``"Gfg"` `: [``4``, ``5``], ``"is"` `: [``6``, ``8``], ``"best"` `: [``10``]} ` ` `  `# printing original dictionary ` `print``(``"The original dictionary is : "` `+` `str``(test_dict)) ` ` `  `# Concatenating dictionary value lists ` `# Using sum() + values() ` `res ``=` `sum``(test_dict.values(), []) ` ` `  `# printing result  ` `print``(``"The Concatenated list values are : "` `+` `str``(res)) `

Output :

```The original dictionary is : {'Gfg': [4, 5], 'best': [10], 'is': [6, 8]}
The Concatenated list values are : [4, 5, 10, 6, 8]
```

Method #2 : Using` chain() + * operator`
This task can also be performed using the combination of these methods. In these, we just use inbuilt function of `chain` for concatenation to list and * operator is used to access all the list values into one.

 `# Python3 code to demonstrate working of ` `# Concatenating dictionary value lists ` `# Using chain() + * operator ` `from` `itertools ``import` `chain ` ` `  `# initializing dictionary ` `test_dict ``=` `{``"Gfg"` `: [``4``, ``5``], ``"is"` `: [``6``, ``8``], ``"best"` `: [``10``]} ` ` `  `# printing original dictionary ` `print``(``"The original dictionary is : "` `+` `str``(test_dict)) ` ` `  `# Concatenating dictionary value lists ` `# Using chain() + * operator ` `res ``=` `list``(chain(``*``test_dict.values())) ` ` `  `# printing result  ` `print``(``"The Concatenated list values are : "` `+` `str``(res)) `

Output :

```The original dictionary is : {'Gfg': [4, 5], 'best': [10], 'is': [6, 8]}
The Concatenated list values are : [4, 5, 10, 6, 8]
```

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